The present invention relates to an LCD (liquid crystal display) device, and more particularly, to an LCD device which is capable of minimizing a screen defects due to wrinkling of an optical sheet resulting from infiltration of moisture thereinto, by preventing moisture from being introduced into the LCD device.
Generally, LCD devices have a wide range of application in portable computers such as notebook and laptop computers, office automation (OA) equipment, audio/video devices and so on because they are light, thin and have low power consumption characteristics.
Typically, the LCD device has a function that displays images on a screen by controlling of optical transmittance according to video signals applied to a plurality of controlling switching devices aligned in a matrix format.
The LCD device includes a liquid crystal panel having a color filter as a front substrate and a thin film transistor array as a rear substrate, which are disposed to face each other, and a liquid crystal layer interposed between the substrates, and a drive unit supplying scanning signals and image information to the liquid crystal panel to operate the liquid crystal panel. Also, front and rear polarizers are disposed at front and rear portions of the liquid crystal panel, respectively.
Because the LCD device is a non-spontaneous light emitting device that cannot emit light spontaneously, comparing with a CRT (cathode-ray tube) or an LED (light-emitting diode), a light source such as a lamp, etc. is employed for supplying light onto the liquid crystal panel so as to implement an image display. Thus, the transmission type LCD device is provided with a back light assembly as the light source supplying light onto the liquid crystal panel.
Typically, the liquid crystal panel and the back light assembly are fabricated through separate processes and then physically coupled together in an integrated form as a module, for thereby avoiding light leakage therebetween and for better resisting an external impact. Such coupling together of the liquid crystal panel and the back light assembly is implemented by a case. Typically, the case is coupled in a form that covers the back light assembly including edges of the liquid crystal panel.
FIG. 1 is an exploded perspective view showing a related art LCD device, and FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1.
As shown in FIGS. 1 and 2, the related art LCD device includes a liquid crystal panel 100, a back light assembly 101 provided with a lamp 105 for supplying light onto the liquid crystal panel 100, a main support frame 102 receiving the liquid crystal panel 100 and the back light assembly 101, a lower cover 103 disposed at an opened long side of the main support frame 102 where the lamp 105 is disposed for enabling access for replacement of the lamp 105, and an upper cover 104 covering edges of the liquid crystal panel 100 and the main support frame 102.
The back light assembly 101 includes the lamp 105, a light guide plate 106 guiding the light emitted from the lamp 105 toward the liquid crystal panel 100, an optical sheet 107 located at a front surface of the light guide plate 106 for diffusing and collecting the light, and a reflection sheet 108 located at a rear surface of the light guide plate 106 for reflecting the light emitted from the lamp 105 toward the liquid crystal panel 100.
The LCD device constructed as described above may suffer a problem in that over time a gap can arise due to loosening or deformation of the coupling portions between the liquid crystal panel 100 and the back light assembly 101, and then, moisture may infiltrate into the LCD device, causing defects in the LCD device.
Gaps between the liquid crystal panel 100 and the back light assembly 101 can occur at several locations, but, as shown in FIG. 2, typically occur at the portions indicated at A, B and C. The portions A, B and C are the portions are those locations where gaps can occur due to use of the LCD device.
Here, portion A refers to a gap arising between an outer peripheral surface of the main support frame 102 and an inner lateral peripheral surface of the upper cover 104, portion B refers to a gap arising between an internal stepped portion of the main support frame 102 and a rear surface of the reflection sheet 108, and portion C refers to the gap arising between an inner upper surface of the upper cover 104 and a front surface of the liquid crystal panel 100.
The locations A, B and C provide paths for moisture to infiltrate into the LCD device under a humid environment. Such introduction of moisture can cause the deformation of the optical sheet 107, whereby, when the LCD device is driven, the screen display may be defective. This problem is especially of concern in relation to LCD modules employed in portable devices where exposure to humid conditions as well as conditions promoting condensation of moisture may be encountered.
Also, although not shown in FIG. 2, gaps may also arise at a location where the rear surface of the reflection sheet 108 and the inside of the lower cover 103 contact with each other, thereby acting as a path for moisture infiltration into the LCD device
Moisture is mostly introduced at location A among the above four locations. However, moisture infiltration through locations other than at A cannot be overlooked.
Meanwhile, as it is required for the LCD devices to become increasingly lighter and thinner, related research is being actively conducted. But, these ultra light and thin LCD devices generally use much thinner and lighter optical sheets, comparing with the general LCD device. Accordingly, when moisture is infiltrated thereinto, the optical sheet in such ultra light and thin LCD devices may be very easily deformed, comparing with that in the general LCD devices, thereby deteriorating the quality of a screen display of the LCD device.